Coating compositions such as paints typically include pigments such as titanium oxide in order to enhance visual hide and provide aesthetic effect. The typical coating composition includes a pigment and other solid components dispersed within in a liquid. For example, most paints include a film forming material or binder along with the pigment dispersed within a solvent.
In a paint composition, the pigment is desirably dispersed in the liquid component. When the paint is applied to a substrate, the solvent evaporates leaving behind the solid components. In particular, the pigment and binder coalesce to form a continuous film. The spacing of the pigment particles is important in determining the characteristics of the paint coating. Uniform dispersion of the particles in the final coating is most desirable. Non-uniform dispersion caused by flocculation and/or settling of the pigment phase may result in several undesirable properties such as a non-uniform appearance and spotty coverage. In each of these mechanisms, pigments tend to cling together by agglomerating or clustering. Moreover, in such instances the pigment particles tend to resist subsequent re-dispersion by agitation. This reduces the hiding power of the resulting paint. Hiding power is among one of the most important attributes of paint, and hiding power is determined particularly in white paint by the light scattering effectiveness of the pigment. The light scattering effectiveness of the pigment is in turn highly dependent on the spacing arrangement of the pigment in the dried coating as well as the particle sizes.
Titanium dioxide is perhaps the most widely used pigment in paint applications. However, in order to improve the masking properties of paint compositions, the titanium dioxide must be pretreated with various oxides. Such pretreatment adds to the cost of the titanium oxide making it relatively expensive in comparison to the costs of other paint components. Therefore, there is a need to maximize the beneficial aspects of titanium dioxide, while minimizing the amount used. Enhanced light scattering occurs when the titanium dioxide pigment particles have a diameter of about 200 to 300 nm and are uniformly spaced about the same distance apart. Most commonly, particulate TiO2 in the range of 100 nm to 400 nm is utilized in conventional paint. Several prior art methods exist for improving the dispersion of pigments in paints. Various techniques have been attempted and used in the art to promote an even spacing and distribution of the pigment in the coating. For example, “extender” pigments have been used to increase pigment spacing. U.S. Pat. No. 7,727,323 provides another method is which nano-sized zinc oxide particles are used to decrease flocculation. Although these techniques work reasonably well, improvements to further reduce flocculation are still desired.
Accordingly, there is a need for titanium oxide paint compositions with improved processing characteristics and reduced costs.